Photovoltaic modules, devices, or cells, can include multiple layers (or coatings) created on a substrate (or superstrate). For example, a photovoltaic device can include a barrier layer, a transparent conductive oxide layer, a buffer layer, and a semiconductor layer formed in a stack on a substrate. Each layer may in turn include more than one layer or film. For example, a semiconductor window layer and a semiconductor absorber layer together can be considered a semiconductor layer. Additionally, each layer can cover all or a portion of the device and/or all or a portion of a layer or a substrate underlying the layer. For example, a “layer” can include any amount of any material that contacts all or a portion of a surface. Cadmium telluride has been used for the semiconductor layer because of its optimal band structure and a low cost of manufacturing.
In order to electrically connect the photovoltaic device, a back contact layer can also be used. The back contact layer can include an electrically conductive material, such as a metal, deposited onto the semiconductor layer. The back contact material is typically a metal selected for sufficient adhesion to the semiconductor layer and minimal formation of a back contact barrier that can affect the current-voltage characteristics of the photovoltaic device.
Prior to depositing or forming the back contact layer on the semiconductor layer of a photovoltaic device, it may be desirable to remove surface contaminants from the semiconductor layer. Surface contamination includes oxidation of the semiconductor layer, adsorption of hydrocarbon and/or carbonates and/or other organic and inorganic contaminants on the semiconductor layer, for example. Contaminants formed on the semiconductor layer may affect an interface between the semiconductor layer and the back contact layer. A poor interface between the semiconductor layer and the back contact layer may have an undesirable effect on the photovoltaic device, and specifically on VOC and ROC. Known methods of removing contaminants from the surface of the semiconductor layer may negatively affect a grain boundary and/or lattice of the crystals forming the semiconductor layer. It would be desirable to develop a more effective method to remove surface contaminants from a semiconductor layer of a photovoltaic device prior to depositing or forming a back contact layer to improve a performance of the photovoltaic device.